U.S. Pat. No. 3,231,065, in the name of Kaminski, et al, discloses an article feeding apparatus which is a substantial improvement over most intermittent feed conveyers, which are of the rotary type wherein the articles to be operated upon are fed in succession onto a conveyor wheel which then indexes intermittently through a series of positions at which a number of operations may be carried out upon the article. In order to provide for high speed production in a feed conveyor of the rotary type it is necessary that the feed be extremely accurate such that each articles is presented in its indexed position in exactly correct orientation for the operation which is to be performed upon it. This is difficult to accomplish because of the problem of inertia in intermittent feed apparatus. The turret type of apparatus requires a relatively heavy element to be started up from a stand still, moved through a certain part and brought to a stop. This requires complicated apparatus and excessive amount of power. The article feeding apparatus of U.S. Pat. No. 3,231,065 was a substantial improvement over the prior art because it provided a feed mechanism whereby there is a minimum of inertia in the moving parts such that starting and stopping intermittently did not present a serious problem. It furthermore provided an apparatus wherein the intermittent feed could be extremely accurate without the need for complex mechanism which had been theretofore necessary for accurate positioning of the workpieces.
While the article feeding apparatus of U.S. Pat. No. 3,231,065 has generally proven to be satisfactory, the art is always seeking to improve upon what has gone on before in order to develop new article feeding apparatus which are capable of higher speed and low cost article production. More particularly, the art has continually sought to develop improvements in the non-stretchable belt passing around the drums, as well as in the means to accurately adjust the driving sprocket on the driving drum to align the articles on the belt with the tool stations. Additionally, the art has continually sought improvements in the idler take-up drum for use with the article transfer belt so as to eliminate abrasion on the back side of the belt due to slippage and reduce the weight, i.e., inertia, of the idler each time the belt intermits to transfer the articles, which is particularly important at high speeds.
FIGS. 4A and 4B are exemplary of problems attributable to prior art belts. The belt 10 of FIGS. 4A and 4B is made endless by riveting (FIG. 4B) or welding (FIG. 4A), if metallic, or adhesively secured if non-metallic. Holes 12 are provided along at least one edge of the belt 10 for accurate indexing without slip. However, a number of problems have been evidenced with this belt construction. For example, in the metallic belt 10, the metallic material must be selected with high fatigue resistance. This material is required to withstand the flexural stress imposed as the belt 10 wraps around the drums. When this material is welded (FIG. 4A), the metal in the weld area becomes annealed, as at 13. The boundary layer between the annealed weld metal and the non-annealed parent metal becomes embrittled and failure occurs in this area and the belt splice breaks.
The prior art has developed a riveted joint 15 for metallic belts 10, as shown in FIG. 4B, which eliminates the embrittled metal problem. However, the belts 10 now fail in service due to fatigue failure in the basic metal propagating cracks 14 from the edges of the belt 10 into the holes 12 along the edges of the belt 10 and finally into the article carrying apertures 16 in the center of the belt 10. This failure occurs because the fatigue limit, in turns of number of bending cycles (around the drums), has been reached. Additional wear areas on the belt 10 are shown at 17.
The useful service life of the belt 10 can be improved by increasing the diameter of the driving and idler drums in order to reduce the bending stress on the belt. This, however, increases the mass of the components which must be intermittently started and stopped, causing undue load on the driving mechanism due to increased inertia. Further, as the driving drum diameter is increased, positioning accuracy is decreased.
Non-metallic, non-stretchable belts overcome the fatigue failure problems of metallic belts 10. However, edges holes 12 in a non-metallic belt 10 cooperating with sprocket teeth in the driving drum, do not provide the required positioning accuracy. This is so because the edge holes 12 are resilient and yield against the pressure of the sprocket teeth on the driving drum. Attempts to provide metallic bushings in the edge holes have not provided successful and have greatly increased the cost of the belt 10.
The prior art has endeavored to utilize the teachings of U.S. Pat. No. 3,812,953, in the name of Marvin W. Maschke in an attempt to solve the aforementioned problems attributable to non-metallic, non-stretchable belts. However, this has not proven successful since it has been found that the edge of the article apertures in the belt will yield instead of properly seat over the locating plugs. Further, the Maschke driving or idler drums are expensive construction particularly with articles that are other than round.